1. Field of Invention
This invention relates to microwave antennas and more particularly to a frequency-scanned antenna.
2. Description of the Prior Art
A frequency-scanned antenna is typically comprised of a waveguide bent in the shape of a serpentine such that the antenna has a plurality of bends on its left side and a plurality of corresponding bends on its right side. Moreover, the displacements between the corresponding bends are equal. A plurality of radiators are usually connected to the bends on one side in a manner that prevents the waveguide form occluding the radiators. Since the radiators are connected to the bends on one side and the displacements between the corresponding bends are equal, the radiators are evenly spaced along the length of the waveguide.
The scanning aspects of the antenna are predicated upon the electrical length (wavelengths) of the waveguide being a function of the frequency of a wave that propagates through the waveguide. In other words, the waveguide is a delay line that has an electrical length which is a function of the frequency of applied excitation.
Typically, the excitation is applied to an input end of the waveguide thereby providing to the radiators respective signals that each comprise a predetermined percentage of the excitation. When the excitation has a frequency which is a function of time, the signals all have phase angles which are functions of time. The signals cause the radiators to provide radiation that combines to form a beam with a pointing angle which is a function of time. The antenna described hereinbefore is of a type which is the subject matter of pages 13-10 through 13-16 of "Radar Handbook" by Merrill I. Skolnik, published by McGraw Hill Book Company.
The antenna generally comprises a multiplicity of expensive, machined components that are difficult to assemble. Additionally, the components cannot be assembled to be mechanically rugged enough to survive an atomic blast at a hardened missile site, for example.
Frequency-scanned antennas that are inexpensive, reliable, easily assembled and mechanically rugged have heretofore been unknown in the prior art.